Silicone rubber has found many uses in applications as the material for protective articles for the human body because silicone rubber exhibits a non-irritating effect on the human skin. One of these many applications is as the transparent material for face masks which are used throughout industry and in the military. However these silicone rubber face masks have exhibited several problems which have largely nullified their advantage of non-irritation. One problem is that the transparent masks are easily scratched and therefore quickly lose their good optical qualities where they are employed in areas containing significant concentrations of abrasive particles such as in outdoor activities, particularly in the military. Another problem is that the silicone masks are permeable to many organic substances which are irritating or even toxic thereby limiting their use in many industrial applications, and in the military as masks to protect against the effect of certain agents used in chemical warfare.
Many materials have been considered as coatings for the silicone rubber in attempts to overcome the deficiencies of silicone rubber as a face mask material. However a problem with these coatings has been encountered due to the requirement that the silicone rubber retain its good elongation properties at low temperatures. A scratch resistant coating which cannot bend and stretch with the silicone rubber would tend to crack and separate from the silicone rubber mask.
Polyurethanes could be an ideal coating for silicone rubber face masks. Polyurethanes provide the abrasion resistance required to prevent stratching of the lens portion of the face mask and at the same time present a barrier to the diffusion of many organic compounds through the face mask. Polyurethanes are also highly flexible even at low temperatures. Unfortunately, polyurethanes have not heretofore been suitable for use as coatings for silicone rubber because they could not be satisfactorily bonded to silicone rubber.
A process which would render silicone rubber adhesive to polyurethane coatings and therefore lead to a good bond between silicone rubber and polyurethanes would be of a great advantage.